1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof. In particular, the present invention relates to a semiconductor device where a semiconductor element provided over an upper surface of a substrate can be electrically connected to a back surface of the substrate with the substrate interposed therebetween, and a preferable manufacturing method thereof.
2. Description of the Related Art
In recent years, by forming a semiconductor element over a rigid substrate such as a glass substrate, a semiconductor device has been actively developed for use in a display such as an LCD or an organic EL display, a photoelectric conversion element such as a photo sensor or a solar cell, or the like. In addition, by forming a semiconductor element using a Si wafer, a semiconductor device for use in a cellular phone and the like has been developed. Moreover, a semiconductor device which transmits and receives data without contact (also referred to as an RFID (Radio Frequency Identification) tag, an ID tag, an IC tag, an IC chip, an RF (Radio Frequency) tag, a wireless tag, an electronic tag, or a wireless chip) has been actively developed. In any case of using a rigid substrate such as a glass substrate, a semiconductor substrate such as a Si substrate, and the like for manufacturing such a semiconductor device, reduction in thickness, miniaturization, or the like of the semiconductor device is required.
As a method for thinning a semiconductor device, for example, a method for grinding and polishing a substrate, a method for etching a substrate by using a chemical reaction, or the like (for example, see Reference 1: Japanese Patent Application Laid-Open No. 2002-87844) is performed.
However, generally, in a case of forming a thin substrate with the use of the above method, an upper surface of a substrate is provided with a semiconductor element, but a method for forming electrical continuity between the semiconductor element that is provided over an upper surface of a substrate and a back surface thereof has not been established yet. Therefore, although thin semiconductor elements can be stacked, a lead wiring and the like are necessary in a case of electrically connecting the stacked semiconductor elements; thus, it has been difficult to further increase an added value thereof.